Considerable effort has been expanded over the last couple of decades to develop point-of-care diagnostic tests. The glucose meter is one such successful product used by millions daily around the world to monitor the sugar level in their blood. A second is the home pregnancy test kit. Both devices are low cost, easy to use, highly accurate and reliable.
The pregnancy test kits utilize Lateral Flow Immunochromatographic Assay Devices more commonly referred to as Lateral Flow Test Strips or simply Test Strips. Such test strips are available in the market also for detecting other proteins or molecules in biological fluids. However, their success as products is limited for a number of reasons, such as that their signal fades with time, their sensitivity it too low or because they are not simple enough to use.
The gold standard for the detection of proteins is ELISA (Enzyme Linked Immunosorbent Assay) which requires a number of reagents to be applied sequentially to the detection site. Test strips cannot perform ELISA because they are limited to only one fluid, typically the sample fluid, which precludes an enzymatic reaction that requires, at the very least, the introduction of a substrate. Test strips incorporating more fluids have been commercialized but these devices are no longer simple to use.
U.S. Patent Application Publication No. 2013/0078711 discloses the use of a paper based microfluidic valve (PBMV) for achieving these goals by being able to perform ELISA on modified Lateral Flow Test Strips.
What is needed to make test strips broadly commercially successful is to be able to modify them so that more fluids are used for the assay but those reagents flow autonomously and entirely transparently to the user, thus maintaining the strip test's simplicity of use, while producing more valuable results. There remains a need therefore, for microfluidic devices that meet these needs.